Photometer.



C. H. SHARP. PHOTOMETER. APPLICATION FILED Aums. Isls.

Patented Mar. 1l, 1919 2 SHEETS-SHEET l.

. I n I I I I I I I I I I I C. .H. SHARP.

PHoTomfER.

u APPLICATION FILED AUG.26. l9l6. 1,297,260.

5 (L inventor Patented Mm. 11,1919. v

UNITED STATES PATENT orne v fr CLAYTQN n. SHARP, 0F TlHl'f-lllA PLAINS, NEW YORK, lASSIIGANOR TO GENERAL ELECTRIC COIPANF, A CORPORATION 0F NEW'YORK.

rnoTomE'rEn.

l To' alllwhom -it may concern:

Be it known that I, CLAYTON H. SHARr, a cltlzen of the United Sta-tes, residing in White Plalns, county of I Vestchester, and

State of New York,'have invented acertain new and useful Photometer, of lwhich t-hev following is a specification. p.

This invention relates to improvements in photometers for the measurement of illuminatlon, and has for its principal 'object the simplification o f devices whereby it may be l `made-portable, small and cheap. A further movable parts.

line 2-2 of Fig. 1.' f.

Specification land accompanying Fig. 5' is a plan view of a modified. form of portable of photometer. embodying the invention.

6 is a sectional view on thedfine 6 6 ofFlg. 5.

Fig. 7 is a plan View of another modified.-

fo'rm of photometric element.

Fig. 8 isa similar View' of still another modification, .said section being taken on the lineS--S lof Fig. 9. F `g. 9 is a sectional View taken on line 9-9' of Fig. 8.

Fig. 10 is a plan View of.a complete form photometer embodying the in'- vention. y

-. Fig. 11 is a sectional view thereof taken on the 'line 11--11 of Fig. 10, and

Fig. 12 is-a diagrammatic view of electric connections' suitable for the structure illustrated in Figs. 10 and 11.

In all of the views like parts are designated by the same reference characters.

Figs. 1, 2 and 3 represent a simple embodiment of the invention., The device asillustrated is inclosed in a casing 1. This casing is preferably of rectangular sha.pel and itsv length considerably exceeds its width or depth. Within this casing is a suitable source of illumination. This source of illulmination may be an incandescent 'electric lamp adjusted so as to give a suitable candle 'is'considerably longer lthan vit is wide, and

drawings a photometer Atransparent glass.

l Specieatfon ofLe'tt-ers Patent. Patented Mar. 1 1, 1919. Appli'oation'led vAugust i385 1916. Serial No. 116,965. v

power. Instead of an electriclamp, any other form ofllamp may be employed, previded` it gives a suitable candle power.

Associated with the casing 1, in the embodiment chosenfor illustration, locatedon the upper surface thereof, is a photometric element 3. This element is' substantially opaque, but with a white reflecting surface, so as to reflect the illumination to the eyeofthe observer. Within this element is a comparison aperture Y4. This. comparison aperture is shown vas extending throughout the length-of the photometric element. It

is also in alinemfent with Ithe source lof illumination'. The edge of. the aperture is 'showna's serrated or saw toothed. Ad'acent j to the source of illumination is a. di using partition 5, which may be made of semi- This necessary but it is desirable. l

The hotometric element, in this embodi-m ment Q this invention, is shown as made of a transparent support 6, preferably a sheet of transparent glass. The'photometrlc ele- 'ment is completed by means of a sheet of p cardboard or similar material -with a diffusely reflecting surface applied to and's'upl lported by the transparent support 6, and aving thev comparison aperture cut wlthin.

to be measured. For measuring illumination by tungsten lamps, I prefer to. use

to produce a color matchwith the light fromkk closed' by a. diffusingN -surface 7, which iS preferably made of unglazed paper, which" is quite thin and of a diffusing nature. 'This unglazed paper preferably extends o'qer the whole surface of the cardboard, so. that1all-. ll00 of the surface of the photometric element has the same texture.

'Associated with the photometric element is ascale 8'. The interior of the casing. 1s

preferably provided with a coating, the sidesy v105 andl bottom being coated white, while'thef illumination end'opposite the source of coated black. y

In operation the device 1s placed v6o-Y partition is 1101275 so y The color ofthe cardboard and consequently the'color of the reflecting surface will be.'

' chosen in connection with the light which 1s l white. For measuring daylight I prefer f to use a cardboard of yellowish tinge so as atutherl point where the illumination is to be meas- 11o varies in respect to .fits distance from thel ured, in such a position that the photometric element may be observed. W'hen'this is done j the interior of the 4casing will be illuminated by the lamp 2, and the comparison aperture will be illuminated from the insideof the, casing, while the outside of the photometric.A

element will be illuminated by the illumination, which is to be measured. The operator may then observe the illumination on the photometric element, Whichis constant throughout its length, and the illumination through the comparison aperture, which source of illumination 2. Atthe point Where these two separate ppints of illumination are of the same value the amount of illumination in foot candles, or other sulitable'units will appear uponthe scale 8, which it istov be understood has been suitably calibrated for this purpose. l

In the embodiment chosen for illustration,

the light from the Alamp will illuminate the diffusing surface 7 to' a degree,whicli will vary from the end nearest the lamp to the other end of |the casing., Theillumination, therefore, Will gradually Vary while the other portion of the photometric element will be uniformly illuminated from the source of illumination outside of the casing',

which is to be measured.

By making the comparison aperture with an irregular or serrated edge, the'observer will have no difficulty in very accurately determining where the point of equal illu-inination occurs. On the end of the aperture adjacent to the lamp 2 the aperture will appear brighter than the outer surface of the photometric element, while the other end of y the aperture will be darker. At some point between these the outside illumination reflectedto the eye from' the photometric element and the inside illumination. passingy through the comparison aperture are equal in value, and at this point 'it is difficult for the eye to distinguish the edges of the :ipertiirc. This is' the point which the eye must` seek in using the instrument, and this is the. point which will indicate the amount of illuniinationuponthe scale 8.

In order to adapt the instrument to actual measurement ni' illumination, it is necessary to calibrate itf` This may conveniently be done in the following manner :-A\ standardI lamp `which gives an exactly known candleA power is so located as to produce a known illumination on the surface ofthe photometric element of the iilistrunient. "With a given current or a given voltage held constant on the lamp Qwithin thecasingthe eye vof the observer seeks the point'of balance asV already described. At this point he puts a mark which is numbered to agree With the known value of the exterior illumination. The exteriorl illumination is then changed to another known value and the process is re- `l'ar to that illustrated .in Fig. 1.

" closed by a, diifi'ising 4which is measured.

points aneiitire scale may be established'.

p eated.- By (taking a sufficient vnumber of l Fig. -1 shows a modification of the invention,V in which the comparison aperture t is in the form of a plurality of circular openings so arranged as to produce an irregular edge. Each circular opening constitutes a.

vsmall comparison aperture in the photometric element., These apertures are so distributed along the photome'tricelement that a small portion of each aperture corresponds to every distance along the /pliotometric element. therefore,`tliey produce anneiiect simi- IFigs. 5 and 6 illustratefa modification of the invention in which the vphotometric ele- ;ment is" located at the bottom of the easing,

the top of the casing being open. The coin-l parison aperture is-entirely'open andfis not surface as that illustrated'iii Figs; land 2. l i .fi

In using this instruin'ent itis placed above thev surface, the illumination or brightness of which is to be ineasi'ired', "and" the observer looks'through the casing and also. through the comparison'aperture; The inner surface of the photometric element being illuminated from the lamp 2b to a degree varying with the distance from such lamp, "the" observer' may determine at what point the illumination balancesand this is `the `point Which will. be indicated upon the scale-as showing.

the `amoiint of illun'iination` o'rl brightness F'g. 7 is a'inodiiication of the invention'in which the" photon'.';,-.;ific" element 361s com,

posed of'a sheet oi cardboard havingia reci.'`

tangular slit or opening 4c which constitutes the con'ip'ariso'n aperture. Thisaperture isr adapted to extend longitudinally in relation to the casing'.

Figs. 8' and Qillustrate an embodiment of the invei'iiion.I in which 'they obsei'vatioi'i is taken through the sideof `the casing; Iii this embodiment the comparisonaperture v-ll is made inthe form of'fa series of spared openings.' On the opposite `side ofthe' casing are equally spaced observation'apertures 129.

The inside of the casing is provided withvv the white diffusing. surface, hereiubet'oi'e described. In the use o f this device, the casing is held ato'n'e'si'de ofthe siirface,-the illumif nation or brightness of which' is to be meas-x uredli andl 'the kobserver successively looks 'throii'gh the apertures 12, seeing the surA face to be illuminated through the apertures 4d and also the illumination fromythe lamp on the inner wall-of the casing surrounding Figs. l0 and 11 illustrate a. practical embodiment. of my invention adapted to produce a small portable photometer. The device is located within a. carrying case 18 shown as having a cover 14 and a suitable carrying handle. The case .is provided with a partition 15 below which is a battery 16; on the partition is a suitable switch 17, a rheostat 18 and a voltmeter 19. The casing 1 is suitably attached to the partition by means of a clasp 20. Suitable wire connections are made, as shown in Fig. 12, from the battery to the switch, the lamp 2,.volt meter 19 and rheostat 1S. Ey means of the rheostat a current of given voltage registered on the voltn'ieter may bo caused to flow through the lamp. The candle power o't' the lamp will depend upon the voltage and the operator may adjust the position of the. moving element of the rheostat so that the vol-tage. and candle power of the. lamp are constant. The device may be placed anywhere lthe illumination' of which it is desired to measure, and the amount of such illumination will be indicated upon the scale in the manner hereinbetore described.

In some instancesit may be desirable to measure more Jfeeble illumination or brightness. In Fig. 2 is shown an attachment permitting this to be. done. ln the embodiment chosen for illustration this attachment comprises a diaphragm 21 having an aperture. This aperture will permit a reduced amount ot illumination from the lamp Q, which enters the casing 1. it tl i aperture is proporly proportioned, the same scale 8 may be' employed, dividing or multiplying it by a suitablel constant.

' The character and material of. which the photometric element is made nvill vary in accordance with the situation. The color of the photometric element. may be changed in accordance with the color oi light and ins tensity ot' the light. which is to be measured. For example, in measuring daylight, a paper with a yellowish tint may be einployed covering` the plmtometric. surface so that `two results will be accomplished-first, the brightness oi the surface will be reduced to such a value that it will be comparable with the brightness of the con'iparison apertureand second. the. color of the reiieeted light from the photometric surface. will be made to correspond to the color of thelight transmitted through the comparison aper ture, the latter condition being onedesirable for accuracy in observz-itions.

The extent of the range ot use ot' the instrument may be increase-d by changing the character of the. retlecting surface ot' the photometric element-for example, a gray paper having' a low coeliieient ot' reflection may be used to measure the illuminations of high value.

In accordance with the provisions ot' the patent statutes i l avevv described t' ciple of my invention, together wi.. ,A paratus which i i consider 'to repre" the best embodi. thereof. but lf desireto have it under od that the apjgjJara-tus shown is merel;i illust tive. and that the invention may be carried out in other Ways.-

ila-ving now described my invention what now claim as new and desire to secure by Letters Patent, is:

1. A photometer comprising a casing having an. elongated .comparison aperture, a -oi'nparison lamp in said casing adjacent one. end ot said aperture. and a photometric element mounted in said casing to be eX- posed through said aperture and to be illuminated from one end by said lamp and colored to cause the light retiected 'from said element to have the same color value as the light transmitted through the comparison aperture.

A portable photon'ieter comprising a box, 'an elongated inclosed casing set on top of the box and having an elongated comparison aperture in the top ot said casing, a comparison lamp mounted at one end of said casing. a battery in said box, controlling and measuring instruments mount-- ed on the top of said box adjacent said casing and connected to said battery to control and measure the current to said comparison lan1p.'and an elongated photometric element mounted in said casing to be illuminated trom one end by said lamp and extending lengthwise of said casing to be exposed to.' view through said aperture.

This specification signed and witnessed this twenty-fifth day ot August, 1916.

CLAYTON H. SHARP.

Witnesses LnoNann H. DYnn, XV. E. STRONG. 

